(1) Field of the Invention
The present invention relates to a method for fabricating a semiconductor device and a semiconductor device.
(2) Description of Related Art
A semiconductor light-emitting element formed with a low-temperature deposition buffer layer (1986, H. Amano, N. Sawaki, I. Akasaki, and Y. Toyoda: Appl. Phys. Lett., 48 (1986) 353) has been proposed in the related art as this type of semiconductor light-emitting element. A semiconductor light-emitting element to which p-type conductivity control (1989, H. Amano, M. Kito, K. Hiramatsu, and I. Akasaki: Jpn. J. Appl. Phys. 28 (1989) L2112) and n-type conductivity control (1991, H. Amano and I. Akasaki: Mat. Res. Soc. Ext, Abst., EA-21 (1991) 165) are applied has also been proposed. A semiconductor light-emitting element created by applying a highly efficient light emitting layer fabricating method (1991, N. Yoshimoto, T. Matsuoka, T. Sasaki, and A. Katsui, Appl. Phys. Lett., 59 (1991) 2251) has also been proposed.
FIG. 13 shows an exemplary constitution of a group III nitride semiconductor light-emitting element serving as an example of a semiconductor light-emitting element to which the techniques described above are applied. In the drawing, a group III nitride semiconductor light-emitting element 1 comprises a sapphire substrate 2, and a low-temperature deposition buffer layer 3 is deposited on top of the sapphire substrate 2. An n-GaN cladding layer 4, a GaInN light-emitting layer 5, a p-AlGaN barrier layer 6, and a p-GaN contact layer 7 are deposited in succession on the low-temperature deposition buffer layer 3. A p-electrode 8 is deposited on the uppermost p-GaN contact layer 7, and an n-electrode 9 is deposited on the n-GaN layer, thereby forming the group III nitride semiconductor light-emitting element 1.
In a group III nitride semiconductor light-emitting element, represented by the semiconductor light-emitting element constituted as described above, blue light, green light, and white light can be emitted at high intensity. In other types of semiconductor light-emitting element such as AlGaInP and AlGaAs, for example, a substantially identical layer structure can be produced using a substrate having an appropriate lattice constant, and thus a high light-emission efficiency can be realized.
Even in a semiconductor light-emitting element having high light-emission efficiency, if the efficiency with which light is extracted to the outside of the semiconductor light-emitting element is poor, the overall energy conversion efficiency of the semiconductor light-emitting element is also poor. Hence, improvement of the light extraction efficiency is important. One of the causes of poor light extraction efficiency is a semiconductor refractive index which is larger than the refractive index of air. When the refractive index of the semiconductor is larger than the refractive index of air, a large amount of the light emitted by the light-emitting later is reflected totally, thereby becoming sealed in the interior of the semiconductor light-emitting element.
To solve this problem, a method of molding a semiconductor light-emitting element using an epoxy resin or the like having a refractive index between the refractive index of the semiconductor light-emitting element and the refractive index of air is known (see Semiconductor Elements, Revision, Tetsuro Ishida and Azuma Shimizu, Corona, 1980, for example). A method of improving the light extraction efficiency by forming a large number of protrusions at a peak period of 500 nm or more on the surface layer of the semiconductor light-emitting element is also known (see Japanese Unexamined Patent Application Publication 2003-174191, for example). According to the former constitution, the extreme refractive index difference between the semiconductor light-emitting element and air can be reduced, enabling a reduction in total reflection and an improvement in the light extraction efficiency. In the latter constitution, the emitted light is reflected diffusely by the surface irregularities and can therefore be extracted, enabling an improvement in the light extraction efficiency.